(Reuters) - Shares of hospitals and health insurers fell on Tuesday after the U.S. Congressional Budget Office forecast that 14 million Americans would lose medical insurance by next year under a Republican plan to dismantle Obamacare.

"The Street is reacting to the uncertainty around (the bill), and the possibility of" more challenges ahead, said Ana Gupte, an analyst with Leerink Partners in New York.

"There's uncertainty about the potential downside," and whether the plan will become tougher for hospitals before it gets passed, she said.

The Affordable Care Act of 2010, often dubbed Obamacare, expanded medical coverage, aiding hospitals by reducing the number of uninsured patients who could not pay bills.

Hospital stocks fell after the Nov. 8 presidential election of Donald Trump, who vowed to repeal the ACA, former President Barack Obama's signature domestic policy legislation.

The CBO forecast that 24 million people would be uninsured in 2026 if the plan being considered by the House of Representatives were adopted.

Some health policy experts and Wall Street analysts said the report was more draconian than expected, with the uninsured rate declining more quickly than foreseen.

"While the CBO's estimate... is a negative headline for hospitals, we believe that in its current form, the bill's chances of passing are slim," Jefferies analyst Brian Tanquilut said in a research note.

Tanquilut said he believed legislators "will eventually draft a more palatable, diluted version of 'repeal and replace' that would have a smaller impact on the number of uninsured."

“What that means basically is lower volume for the health insurers. It looks like it's going to be the dismantling of the individual insurance market, which again means lower revenues and the loss of the individual market for the most part for the insurers,” said Vishnu Lekraj, an equity analyst at Morningstar.

The Republican proposal would end Obamacare expansion of the Medicaid insurance program for the poor and would replace Obamacare's income-based subsidies with fixed tax credits for the purchase of private insurance.